1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and more particularly to an electrophotographic image forming apparatus of the type capable of forming color images on both sides of a single recording medium substantially at the same time without turning it over.
2. Description of the Background Art
An image forming apparatus of the type described is disclosed in, e.g., Japanese Patent Laid-Open Publication No. 2000-250272. The apparatus taught in this document includes tandem image forming stations each being assigned to a particular color. A first belt or first intermediate image transfer body is held in contact with four photoconductive elements arranged side by side at the consecutive image forming stations. A second belt or second intermediate image transfer body is movable into and out of contact with the first belt. Toner images of different colors are formed on the photoconductive elements in accordance with image data representative of the first side of a document and then transferred to the first belt one above the other, completing a color toner image. The color toner image is then thermally transferred from the first belt to the second belt by heating means associated with the first belt. Subsequently, toner images of different colors are again formed on the photoconductive elements in accordance with image data representative of the second side of the same document and then transferred to the first belt one above the other, forming another color toner image. When a sheet or recording medium is conveyed to a nip between the first and second belts, the color toner images carried on the first and second belts are thermally transferred to and fixed on opposite sides of the sheet at the same time by the heating means.
The conventional image forming apparatus described above is undesirable from the energy saving standpoint because it includes, in addition to the heating means, cooling means for cooling the toner image on the first or the second belt or the toner images on the sheet to temperature below the softening point of toner and protecting the image forming stations from thermal damage. Moreover, the first belt is not cleaned after the image transfer to the sheet. It is therefore likely that color tone is degraded during the next image forming cycle when, e.g., image transfer efficiency is lowered due to the variation of environmental conditions or similar cause.